The keystone of health services research is availability of large databases. Data from single state Medicaid programs have been fruitfully exploited in the past. A recent HCFA research initiative is resulting in a massive multistate Medicaid database encompassing a population of 10 million over a three year period. This research proposes to develop health services research methodology to use the database for monitoring drug safety. A particular focus is upon drug utilization review for drugs which cause adverse reactions not detected by extant monitoring systems. The development of methodology will be achieved through a series of seven specific drug substudies utilizing the multistate database. A second series of six substudieds will monitor the safety of several controversial drugs, improving our understanding of the risks and benefits of these drugs. A final objective in promotion of health services research, which, at low marginal cost, can exploit a massive existing database.